CN103175381A - Process for preparing liquefied natural gas (LNG) by low concentration coal bed methane oxygen bearing copious cooling liquefaction - Google Patents

Process for preparing liquefied natural gas (LNG) by low concentration coal bed methane oxygen bearing copious cooling liquefaction Download PDF

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CN103175381A
CN103175381A CN2013101174364A CN201310117436A CN103175381A CN 103175381 A CN103175381 A CN 103175381A CN 2013101174364 A CN2013101174364 A CN 2013101174364A CN 201310117436 A CN201310117436 A CN 201310117436A CN 103175381 A CN103175381 A CN 103175381A
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heat exchanger
nitrogen
azeotrope
gas
cryogen
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CN103175381B (en
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张武
肖露
任小坤
姚成林
姚占强
王勇
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Technical Institute of Physics and Chemistry of CAS
Chongqing Research Institute Co Ltd of China Coal Technology and Engineering Group
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Technical Institute of Physics and Chemistry of CAS
Chongqing Research Institute Co Ltd of China Coal Technology and Engineering Group
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Abstract

The invention discloses a process for preparing liquefied natural gas (LNG) by low concentration coal bed methane oxygen bearing copious cooling liquefaction. The process for preparing LNG by low concentration coal bed methane oxygen bearing copious cooling liquefaction comprises the following steps: (1), compression and purification process; (2), liquefaction and separation process which comprises a, main procedure process; b, refrigeratory process, wherein the refrigeratory process comprises b1, mixing cryogen process; and b2, nitrogen cryogen process. Nitrogen cryogen sequentially passes through a first level heat exchanger, a second level heat exchanger, a third level heat exchanger and a subcooler for cooling after being compressed and cooled, the nitrogen cryogen after throttling enters an overhead condenser to output cold quantity, and then the gaseous nitrogen cryogen sequentially passes through the subcooler, the third level heat exchanger, the second level heat exchanger, and the first level heat exchanger, the gaseous nitrogen cryogen is warmed gradually to normal temperature, and then flows back to a nitrogen compressor for being circularly used. The mixing cryogen process is used for controlling evaporation capacity at the bottom of a tower, the nitrogen cryogen process is used for controlling condensation capacity at the top of the tower, and independently adjusting purity coefficient and yield coefficient of natural gas products is achieved. The cryogen in a low temperature region only possesses a nitrogen component, and heavy components of isobutane, isopentane and the like do not exist in the low temperature region, and therefore the problems of being free of refrigeration in the process of throttling, or congestion of a cryogen channel are solved.

Description

Low concentration coal-bed gas contains the oxygen cryogenic liquefying and produces LNG technique
Technical field
The invention belongs to the technical field that makes gas or admixture of gas liquefy, solidify or separate by pressurization and cooling processing, concrete produces LNG technique for a kind of low concentration coal-bed gas contains the oxygen cryogenic liquefying.
Background technology
Coalbed methane containing oxygen be the colliery in recovery process for preventing gas explosion and outstanding, the elementary byproduct that guarantees Safety of Coal Mine Production and pump out, its main component is methane, can find out from its component content, and coal bed gas is the energy and the industrial chemicals of outbalance.But because its composition is comparatively complicated, particularly contain aerobic in coal bed gas, it is breakneck combustion-supporting pro-knock agent, restricted the comprehensive utilization of coalbed methane containing oxygen, in practice, in order to save cost, coal bed gas generally enters atmosphere in the coal mining process, causes the profligacy of resource and to environment.
Along with the development of technology, in the field of natural gas is produced in the low concentration coal-bed gas purification, the liquefaction technology of multiple coalbed methane containing oxygen has appearred at present.Publication number is that CN101922850A and CN101929788A disclose respectively a kind of device that utilizes the method for coalbed methane containing oxygen to prepare liquefied natural gas and utilize coalbed methane containing oxygen to prepare liquefied natural gas, the method and device adopt azeotrope to circulate from cascade refrigeration, unstripped gas after purifying is liquefied and separates, obtain the LNG product, although the method and device can utilize coalbed methane containing oxygen to produce natural gas, also have following problem:
(1) unstripped gas (being low concentration coal-bed gas) comes from extraction under coal mine, and the methane content fluctuation is larger, can affect unavoidably the stable operation of liquefaction process, need to adjust device; And in the method and device, the purity of gas product and yield are controlled by evaporation capacity at the bottom of tower and overhead condensation amount respectively, but for heating at the bottom of tower and being that the cooling refrigerant fluid of tower top is with one, therefore can affect overhead condensation amount (yield) when adjusting product purity, can have influence on again evaporation capacity (purity) at the bottom of tower when equally, adjusting product yield;
(2) if the cryogen working conditions of compressor is unstable, can cause heavy constituent (as iso-butane, isopentane) in a large amount of azeotropes to enter the low-temperature space (temperature is lower than-165 ℃) of liquefying plant, cause this section refrigerant temperature lower than its lower conversion temperature, make after throttling temperature raise (namely not freezing), also can cause solidifying when serious, the cryogen passage is stopped up;
(3) after in coal bed gas, methane was suggested, nitrogen oxygen tail gas was emptying in the lower direct re-heat of the operating pressure (0.3MPa) of rectifying column, does not fully reclaim its energy (pressure energy), wastes energy.
In view of this, the present invention is intended to explore a kind of low concentration coal-bed gas and contains the oxygen cryogenic liquefying and produce LNG technique, this low concentration coal-bed gas contains the oxygen cryogenic liquefying and produces purity and the yield that LNG technique not only can independently be adjusted gas product, and can prevent that the cryogen passage from stopping up, and improve using energy source.
Summary of the invention
The object of the present invention is to provide a kind of low concentration coal-bed gas to contain the oxygen cryogenic liquefying and produce LNG technique, this low concentration coal-bed gas contains the oxygen cryogenic liquefying and produces purity and the yield that LNG technique not only can independently be adjusted gas product, and can prevent that the cryogen passage from stopping up.
For realizing above-mentioned technical purpose, the invention provides following technical scheme:
A kind of low concentration coal-bed gas contains the oxygen cryogenic liquefying and produces LNG technique, comprising:
1) compression cleaning procedure: be purified coalbed methane containing oxygen after low concentration is contained the compressed purification of oxygen coal seam unstripped gas;
2) liquefaction separation circuit: comprise main flow technique and refrigeration process;
A. main flow technique: will purify coalbed methane containing oxygen successively by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler heat exchange refrigeration, and enter rectifying column after throttling, reboiler outlet at the bottom of being arranged on rectifying tower obtains liquefied natural gas, the tower top of rectifying column obtains nitrogen oxygen tail gas, and utilizes the overhead condenser of rectifying column tower top setting to separate out a small amount of methane component that contains in nitrogen oxygen tail gas;
B. refrigeration process: comprise azeotrope technique and nitrogen cryogen technique;
b 1. azeotrope technique: azeotrope is compressed, enter the heavy hydrocarbon separator after cooling is separated into gas-liquid two-phase, wherein the gas phase azeotrope is successively by after first-class heat exchanger and secondary heat exchanger cooling, enter liquid at the bottom of the reboiler heating tower who is positioned at the bottom of rectifying tower, after throttling, the gas phase azeotrope is utilized by three grades of heat exchangers, secondary heat exchanger and first-class heat exchanger output cold and circulating reflux to azeotrope compressor cycle successively; The liquid phase azeotrope cool by first-class heat exchanger and throttling after converge together with first-class heat exchanger with the gas phase azeotrope that refluxes and be back to the utilization of azeotrope compressor cycle;
b 2. nitrogen cryogen technique: the nitrogen cryogen is compressed, cool by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler successively after cooling, nitrogen cryogen after throttling is entered overhead condenser output cold, and then the nitrogen cryogen with gaseous state is back to the utilization of nitrogen compressor cycle by subcooler, three grades of heat exchangers, secondary heat exchanger, first-class heat exchanger cascade raising temperatures successively to normal temperature.
The temperature of the purification coalbed methane containing oxygen that further, obtains through described compression cleaning procedure is that 40 ℃, absolute pressure are 0.42MPa.
Further, described main flow technique comprises the steps:
a 1. will purify coalbed methane containing oxygen successively by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler heat exchange refrigeration, and through forming the mixture of condensate liquid and gas after throttling;
a 2. the purification coalbed methane containing oxygen enters rectifying column from the middle part of rectifying column, at the bottom of condensate liquid flows to tower downwards, and a small amount of nitrogen oxygen tail gas that upwards volatilizees and carry, flow out from condensate outlet after heating by reboiler, and obtaining temperature at condensate outlet is 0.32 ~ 0.36MPa, methane concentration more than or equal to 99% liquefied natural gas for-143.5 ℃, absolute pressure, this liquefied natural gas is by three grades of heat exchanger heat exchange and reach temperature and be-155 ~ 160 ℃, pressure is storage with pressure after the supercooled state of 0.243MPa, obtains the finished product natural gas;
a 3. the tower top of rectifying column obtains nitrogen oxygen tail gas separate out a small amount of methane component of carrying through overhead condenser after, enter again decompressor and expand after the subcooler re-heat, be expanded to nitrogen oxygen tail gas after 0.15 ~ 0.18MPa successively by subcooler, three grades of heat exchangers, secondary heat exchanger and the first-class heat exchanger re-heats regeneration gas as the compression cleaning procedure to the normal temperature.
Further, step b 1In, the initial pressure of azeotrope is 0.26MPa,, enters the heavy hydrocarbon separator after cooling and is separated into gas-liquid two-phase to 3.2-3.8Mpa through the azeotrope compressor compresses;
After wherein the gas phase azeotrope is cooled to-120 ℃ by first-class heat exchanger and secondary heat exchanger successively, enter liquefied natural gas at the bottom of the reboiler heating tower who is positioned at the bottom of rectifying tower, self being cooled to-148 ℃, is that the gas phase azeotrope of-160 ℃ utilizes by three grades of heat exchangers, secondary heat exchanger and first-class heat exchanger output cold and circulating reflux to azeotrope compressor cycle successively with temperature after throttling;
The liquid phase azeotrope is cooled to-50 ℃ by first-class heat exchanger, and converges together with first-class heat exchanger with the gas phase azeotrope that refluxes after throttling and be back to the utilization of azeotrope compressor cycle.
Further, step b 2In, the initial pressure of nitrogen cryogen is 0.35MPa, through nitrogen compressor compresses to 3.2 ~ 3.5MPa, be cooled to-172 ℃ by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler successively after cooling, the temperature of nitrogen cryogen is 0.4MPa for-182 ℃, absolute pressure after throttling, enter overhead condenser output cold, then the nitrogen cryogen with gaseous state is back to the utilization of nitrogen compressor cycle by subcooler, three grades of heat exchangers, secondary heat exchanger, first-class heat exchanger cascade raising temperatures successively to normal temperature.
Further, described azeotrope is the mixture of nitrogen, methane, ethene, propane, isopentane.
Beneficial effect of the present invention is:
Low concentration coal-bed gas of the present invention contains the oxygen cryogenic liquefying and produces LNG technique, by refrigeration process being divided into relatively independent azeotrope technique and nitrogen cryogen technique, and by evaporation capacity at the bottom of the tower of azeotrope technology controlling and process rectifying column, overhead condensation amount by nitrogen cryogen technology controlling and process rectifying column, can independently adjust purity and the yield of gas product, and the cryogen of low-temperature space only has the nitrogen component, there are not the heavy constituents such as iso-butane, isopentane, do not freeze thereby solve throttling, or cryogen passage blockage problem.
Expand through decompressor by the nitrogen oxygen tail gas that the rectifying column tower top is obtained, decompressor is emptying at normal temperatures and pressures, thereby fully reclaims the energy of the nitrogen oxygen that backflows, and reaches the purpose of energy-saving and emission-reduction.
Description of drawings
In order to make purpose of the present invention, technical scheme and beneficial effect clearer, the invention provides following accompanying drawing and describe:
Fig. 1 is that low concentration coal-bed gas of the present invention contains the schematic flow sheet that the oxygen cryogenic liquefying is produced LNG process implementing example.
The specific embodiment
Below in conjunction with accompanying drawing, the preferred embodiments of the present invention are described in detail.
At first contain the oxygen cryogenic liquefying and produce a kind of device of producing natural gas of LNG technique and describe being applicable to low concentration coal-bed gas of the present invention.
As shown in Figure 1, this low concentration coal-bed gas contains the device that the oxygen cryogenic liquefying is produced natural gas, comprises main flow system and refrigeration system.
The coal bed gas flow direction of main flow system after purify comprises first-class heat exchanger 1, secondary heat exchanger 2, three grades of heat exchangers 3, subcooler 4 and rectifying columns 5 successively, rectifying column 5 tower tops arrange overhead condenser 6, the interior setting of rectifying column 5 towers is positioned at the reboiler 7 at the bottom of tower, the nitrogen oxygen outlet that rectifying column 5 tower tops arrange is connected with the nitrogen oxygen outlet of overhead condenser 6, and at the bottom of the tower of rectifying column 5, condensate outlet is set, is used for liquified natural gas and flows out.Be provided with choke valve V between the coal bed gas outlet of subcooler 4 and the coal bed gas entrance of rectifying column 5 f, can carry out the throttling cooling to coal bed gas.
Refrigeration system comprises the azeotrope circulatory system and nitrogen cycle system.The azeotrope circulatory system comprises azeotrope compressor 8, azeotrope cooler 9 and heavy hydrocarbon separator 10 successively along the azeotrope flow direction.the gas phase azeotrope outlet of heavy hydrocarbon separator 10 is communicated in the gas phase azeotrope entrance of reboiler 7 successively by first-class heat exchanger 1 and secondary heat exchanger 2, the gas phase azeotrope outlet of reboiler 7 is successively by three grades of heat exchangers 3, secondary heat exchanger 2 and first-class heat exchanger 1 reflux the gas phase azeotrope and are communicated in the azeotrope entrance of azeotrope compressor 8, the liquid phase azeotrope outlet of heavy hydrocarbon separator 10 converges by the rear gas phase azeotrope with refluxing of first-class heat exchanger 1, liquid phase azeotrope and gas phase azeotrope converge by refluxing together with first-class heat exchanger 1 and enter azeotrope compressor 8, make the azeotrope can be recycling.The azeotrope circulatory system also comprises choke valve V 1, the liquid phase azeotrope outlet of heavy hydrocarbon separator 10 is successively by first-class heat exchanger 1 and choke valve V 1Converge with the gas phase azeotrope that refluxes, by choke valve V is set 1, can carry out expenditure and pressure to the liquid phase azeotrope.Be provided with choke valve V between the gas phase azeotrope outlet of reboiler 7 and three grades of heat exchangers 3 2, can carry out the throttling cooling to the gas phase azeotrope.
The nitrogen cycle system comprises nitrogen compressor 11 and nitrogen cooler 12 successively along the flow direction of nitrogen cooling agent, the outlet of the nitrogen of nitrogen cooler 12 is communicated in the nitrogen entrance of overhead condenser 6 successively by first-class heat exchanger 1, secondary heat exchanger 2, three grades of heat exchangers 3 and subcooler 4, the outlet of the nitrogen of overhead condenser 6 refluxes the nitrogen cooling agent by subcooler 4, three grades of heat exchangers 3, secondary heat exchanger 2 and first-class heat exchanger 1 successively and is communicated in the nitrogen entrance of nitrogen compressor 11, make the nitrogen can be recycling, and provide cold to overhead condenser 6.Be provided with choke valve V between the nitrogen entrance of subcooler 4 and overhead condenser 6 3, can lower the temperature to the nitrogen cooling agent.
This low concentration coal-bed gas contains the device that the oxygen cryogenic liquefying is produced natural gas, be set to the azeotrope circulatory system and nitrogen cycle system by refrigeration system, control evaporation capacity at the bottom of the tower of rectifying column 5 and the overhead condensation amount by nitrogen cycle system control rectifying column 5 by the azeotrope circulatory system, can independently adjust purity and the yield of gas product, and the cryogen of low-temperature space only has the nitrogen component, there are not the heavy constituents such as iso-butane, isopentane, do not freeze thereby solve throttling, or cryogen passage blockage problem.
Further, the main flow system also comprises decompressor 13, the nitrogen oxygen outlet of rectifying column 5 is communicated in the nitrogen oxygen intake of decompressor 13 by subcooler 4, the nitrogen oxygen outlet of decompressor 13 enters cleaning procedure by subcooler 4, three grades of heat exchangers 3, secondary heat exchanger 2 and first-class heat exchanger 1 after making the re-heat of nitrogen oxygen successively.By decompressor 13 is set, make it emptying at normal temperatures and pressures, thereby fully reclaim the energy of the nitrogen oxygen that backflows, reach the purpose of energy-saving and emission-reduction.
Further, the condensate outlet of rectifying column 5 is communicated in natural gas storage tank by three grades of heat exchangers 3, makes gas product reach supercooled state, is convenient to store.
Further, azeotrope cooler 9 and nitrogen cooler 12 are water cooler, can satisfy the cooling requirement of azeotrope and nitrogen cooling agent, and it is cooled to design temperature.
Containing below in conjunction with above-mentioned low concentration coal-bed gas device that the oxygen cryogenic liquefying produces natural gas contains the oxygen cryogenic liquefying to low concentration coal-bed gas of the present invention and produces the specific embodiment of LNG technique and elaborate.
As shown in Figure 1, the low concentration coal-bed gas of the present embodiment contains the oxygen cryogenic liquefying and produces LNG technique, comprising:
1) compression cleaning procedure: be purified coalbed methane containing oxygen after low concentration is contained the compressed purification of oxygen coal seam unstripped gas, the temperature of the purification coalbed methane containing oxygen that the compressed cleaning procedure of the present embodiment obtains is that 40 ℃, absolute pressure are 0.42MPa.
2) liquefaction separation circuit: comprise main flow technique and refrigeration process.
A. main flow technique: will purify coalbed methane containing oxygen successively by first-class heat exchanger 1, secondary heat exchanger 2, three grades of heat exchangers 3 and subcooler 4 heat exchange refrigeration, and by choke valve V fEnter rectifying column 5 after throttling, reboiler 7 outlets at the bottom of being arranged on rectifying column 5 towers obtain liquefied natural gas, and the tower top of rectifying column 5 obtains nitrogen oxygen tail gas, and utilize the overhead condenser 6 of rectifying tower 5 top settings to separate out a small amount of methane component that contains in nitrogen oxygen tail gas.
B. refrigeration process: comprise azeotrope technique and nitrogen cryogen technique.
b 1. azeotrope technique: azeotrope through azeotrope compressor 8 compression, enter heavy hydrocarbon separator 10 be separated into gas-liquid two-phase after azeotrope cooler 9 be cooling, wherein the gas phase azeotrope is successively by after first-class heat exchanger 1 and secondary heat exchanger 2 coolings, enter liquid at the bottom of reboiler 7 heating towers that are positioned at the bottom of rectifying column 5 towers, through choke valve V 2After throttling, that the gas phase azeotrope is recycling to azeotrope compressor 8 by three grades of heat exchangers 3, secondary heat exchanger 2 and first-class heat exchanger 1 output cold and circulating reflux successively; The liquid phase azeotrope cools, also passes through choke valve V by first-class heat exchanger 1 1Converge with the gas phase azeotrope that refluxes after throttling that to be back to azeotrope compressor 8 together with the first-class heat exchanger 1 recycling.
The technological parameter of the azeotrope technique of the present embodiment is as follows:
The initial pressure of the azeotrope of the present embodiment is 0.26MPa, enters heavy hydrocarbon separator 10 and be separated into gas-liquid two-phase after azeotrope compressor 8 is compressed to 3.2-3.8Mpa, is cooling; After wherein the gas phase azeotrope is cooled to-120 ℃ by first-class heat exchanger 1 and secondary heat exchanger 2 successively, enter liquefied natural gas at the bottom of reboiler 7 heating towers that are positioned at the bottom of rectifying column 5 towers, self being cooled to-148 ℃, is that the gas phase azeotrope of-160 ℃ is recycling to azeotrope compressor 8 by three grades of heat exchangers 3, secondary heat exchanger 2 and first-class heat exchanger 1 output cold and circulating reflux successively with temperature after throttling; The liquid phase azeotrope is cooled to-50 ℃ by first-class heat exchanger 1, and converge with the gas phase azeotrope that refluxes after throttling that to be back to azeotrope compressor 8 together with the first-class heat exchanger 1 recycling, can satisfy the requirement of producing of liquefied natural gas, and evaporation capacity at the bottom of the tower of control rectifying column 5.
b 2. nitrogen cryogen technique: the nitrogen cryogen will be through choke valve V through nitrogen compressor 11 compression, cool by first-class heat exchanger 1, secondary heat exchanger 2, three grades of heat exchangers 3 and subcooler 4 successively after nitrogen cooler 12 is cooling 3Nitrogen cryogen after throttling enters overhead condenser 6 output colds, then the nitrogen cryogen of gaseous state is back to nitrogen compressor 11 by subcooler 4, three grades of heat exchangers 3, secondary heat exchanger 2, first-class heat exchanger 1 cascade raising temperature to the normal temperature successively recycling.
The technological parameter of the nitrogen cryogen technique of the present embodiment is as follows:
the initial pressure of the nitrogen cryogen of the present embodiment is 0.35MPa, be compressed to 3.2 ~ 3.5MPa through nitrogen compressor 11, pass through successively first-class heat exchanger 1 after cooling, secondary heat exchanger 2, three grades of heat exchangers 3 and subcooler 4 are cooled to-172 ℃, the temperature of nitrogen cryogen is-182 ℃ after throttling, absolute pressure is 0.4MPa, enter overhead condenser 6 output colds, then the nitrogen cryogen with gaseous state passes through subcooler 4 successively, three grades of heat exchangers 3, secondary heat exchanger 2, it is recycling that first-class heat exchanger 1 cascade raising temperature is back to nitrogen compressor 11 to the normal temperature, can satisfy the requirement of producing of liquefied natural gas, and the overhead condensation amount of control rectifying column 5.
The low concentration coal-bed gas of the present embodiment contains the oxygen cryogenic liquefying and produces LNG technique, by refrigeration process being divided into relatively independent azeotrope technique and nitrogen cryogen technique, and by evaporation capacity at the bottom of the tower of azeotrope technology controlling and process rectifying column, overhead condensation amount by nitrogen cryogen technology controlling and process rectifying column, can independently adjust purity and the yield of gas product, and the cryogen of low-temperature space only has the nitrogen component, there are not the heavy constituents such as iso-butane, isopentane, do not freeze thereby solve throttling, or cryogen passage blockage problem.
Further, the main flow technique of the present embodiment specifically comprises the steps:
a 1. will purify coalbed methane containing oxygen successively by first-class heat exchanger 1, secondary heat exchanger 2, three grades of heat exchangers 3 and subcooler 4 heat exchange refrigeration, and through choke valve V fForm the mixture of condensate liquid and gas after throttling;
a 2. the purification coalbed methane containing oxygen enters rectifying column 5 from the middle part of rectifying column 5, at the bottom of condensate liquid flows to tower downwards, and a small amount of nitrogen oxygen tail gas that upwards volatilizees and carry, by flowing out from condensate outlet after reboiler 7 heating, and obtaining temperature at condensate outlet is 0.32 ~ 0.36MPa, methane concentration more than or equal to 99% liquefied natural gas for-143.5 ℃, absolute pressure, this liquefied natural gas is by three grades of heat exchanger 3 heat exchange and reach temperature and be-155 ~ 160 ℃, pressure is storage with pressure after the supercooled state of 0.243MPa, obtains the finished product natural gas;
a 3. the tower top of rectifying column 5 obtains nitrogen oxygen tail gas separate out a small amount of methane component of carrying through overhead condenser 6 after, enter again decompressor 13 and expand after subcooler 4 re-heats, be expanded to nitrogen oxygen tail gas after 0.15 ~ 0.18MPa successively by subcooler 4, three grades of heat exchangers 3, secondary heat exchanger 2 and the first-class heat exchanger 1 re-heats regeneration gas as the compression cleaning procedure to the normal temperature.
Expand through decompressor 13 by the nitrogen oxygen tail gas that rectifying column 5 tower tops are obtained, decompressor 13 is emptying at normal temperatures and pressures, thereby fully reclaims the energy of the nitrogen oxygen that backflows, and reaches the purpose of energy-saving and emission-reduction.
Further, the azeotrope of the present embodiment is the mixture of nitrogen, methane, ethene, propane, isopentane, can satisfy the temperature control requirement in the links that liquefied natural gas is produced, in azeotrope, the proportioning of each component is set according to the demand of actual refrigerating capacity, certainly, azeotrope also can adopt the azeotrope of existing other components, is not repeated.
Explanation is at last, above preferred embodiment is only unrestricted in order to technical scheme of the present invention to be described, although the present invention is described in detail by above preferred embodiment, but those skilled in the art are to be understood that, can make various changes to it in the form and details, and not depart from claims limited range of the present invention.

Claims (6)

1. a low concentration coal-bed gas contains the oxygen cryogenic liquefying and produces LNG technique, it is characterized in that: comprising:
1) compression cleaning procedure: be purified coalbed methane containing oxygen after low concentration is contained the compressed purification of oxygen coal seam unstripped gas;
2) liquefaction separation circuit: comprise main flow technique and refrigeration process;
A. main flow technique: will purify coalbed methane containing oxygen successively by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler heat exchange refrigeration, and enter rectifying column after throttling, reboiler outlet at the bottom of being arranged on rectifying tower obtains liquefied natural gas LNG, the tower top of rectifying column obtains nitrogen oxygen tail gas, and utilizes the overhead condenser of rectifying column tower top setting to separate out a small amount of methane component that contains in nitrogen oxygen tail gas;
B. refrigeration process: comprise azeotrope technique and nitrogen cryogen technique;
b 1. azeotrope technique: azeotrope is compressed, enter the heavy hydrocarbon separator after cooling is separated into gas-liquid two-phase; Wherein the gas phase azeotrope is successively by after first-class heat exchanger and secondary heat exchanger cooling, enter liquid at the bottom of the reboiler heating tower who is positioned at the bottom of rectifying tower, after throttling, the gas phase azeotrope is utilized by three grades of heat exchangers, secondary heat exchanger and first-class heat exchanger output cold and circulating reflux to azeotrope compressor cycle successively; The liquid phase azeotrope cool by first-class heat exchanger and throttling after converge together with first-class heat exchanger with the gas phase azeotrope that refluxes and be back to the utilization of azeotrope compressor cycle;
b 2. nitrogen cryogen technique: the nitrogen cryogen is compressed, cool by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler successively after cooling, nitrogen cryogen after throttling is entered overhead condenser output cold, and then the nitrogen cryogen with gaseous state is back to the utilization of nitrogen compressor cycle by subcooler, three grades of heat exchangers, secondary heat exchanger, first-class heat exchanger cascade raising temperatures successively to normal temperature.
2. low concentration coal-bed gas according to claim 1 contains the oxygen cryogenic liquefying and produces LNG technique, it is characterized in that: the temperature of the purification coalbed methane containing oxygen that obtains through described compression cleaning procedure is that 40 ℃, absolute pressure are 0.52MPa.
3. low concentration coal-bed gas according to claim 2 contains the oxygen cryogenic liquefying and produces LNG technique, and it is characterized in that: described main flow technique comprises the steps:
a 1. will purify coalbed methane containing oxygen successively by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler heat exchange refrigeration, and through forming the mixture of condensate liquid and gas after throttling;
a 2. the purification coalbed methane containing oxygen enters rectifying column from the middle part of rectifying column, at the bottom of condensate liquid flows to tower downwards, and a small amount of nitrogen oxygen tail gas that upwards volatilizees and carry, flow out from condensate outlet after heating by reboiler, and obtaining temperature at condensate outlet is 0.32 ~ 0.36MPa, methane concentration more than or equal to 99% liquefied natural gas for-143.5 ℃, absolute pressure, this liquefied natural gas is by three grades of heat exchanger heat exchange and reach temperature and be-155 ~ 160 ℃, pressure is storage with pressure after the supercooled state of 0.243MPa, obtains finished product LNG;
a 3. the tower top of rectifying column obtains nitrogen oxygen tail gas separate out a small amount of methane component of carrying through overhead condenser after, enter again decompressor and expand after the subcooler re-heat, be expanded to nitrogen oxygen tail gas after 0.15 ~ 0.18MPa successively by subcooler, three grades of heat exchangers, secondary heat exchanger and the first-class heat exchanger re-heats regeneration gas as the compression cleaning procedure to the normal temperature.
4. low concentration coal-bed gas according to claim 3 contains the oxygen cryogenic liquefying and produces LNG technique, it is characterized in that: step b 1In, the initial pressure of azeotrope is 0.26MPa,, enters the heavy hydrocarbon separator after cooling and is separated into gas-liquid two-phase to 3.2-3.8Mpa through the azeotrope compressor compresses;
After wherein the gas phase azeotrope is cooled to-120 ℃ by first-class heat exchanger and secondary heat exchanger successively, enter liquefied natural gas at the bottom of the reboiler heating tower who is positioned at the bottom of rectifying tower, self being cooled to-148 ℃, is that the gas phase azeotrope of-160 ℃ utilizes by three grades of heat exchangers, secondary heat exchanger and first-class heat exchanger output cold and circulating reflux to azeotrope compressor cycle successively with temperature after throttling;
The liquid phase azeotrope is cooled to-50 ℃ by first-class heat exchanger, and converges together with first-class heat exchanger with the gas phase azeotrope that refluxes after throttling and be back to the utilization of azeotrope compressor cycle.
5. low concentration coal-bed gas according to claim 4 contains the oxygen cryogenic liquefying and produces LNG technique, it is characterized in that: step b 2In, the initial pressure of nitrogen cryogen is 0.35MPa, through nitrogen compressor compresses to 3.2 ~ 3.5MPa, be cooled to-172 ℃ by first-class heat exchanger, secondary heat exchanger, three grades of heat exchangers and subcooler successively after cooling, the temperature of nitrogen cryogen is 0.4MPa for-182 ℃, absolute pressure after throttling, enter overhead condenser output cold, then the nitrogen cryogen with gaseous state is back to the utilization of nitrogen compressor cycle by subcooler, three grades of heat exchangers, secondary heat exchanger, first-class heat exchanger cascade raising temperatures successively to normal temperature.
6. according to claim 1-5 described low concentration coal-bed gas of any one contain the oxygen cryogenic liquefying and produce LNG technique, and it is characterized in that: described azeotrope is the mixture of nitrogen, methane, ethene, propane, isopentane.
CN201310117436.4A 2013-04-07 2013-04-07 Low concentration coal-bed gas produces LNG technique containing oxygen cryogenic liquefying Active CN103175381B (en)

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CN105296038A (en) * 2015-11-27 2016-02-03 中煤科工集团重庆研究院有限公司 Oxygen-bearing coal-bed gas low-temperature concentration method and device for implementing method
CN105349195A (en) * 2014-08-19 2016-02-24 中国海洋石油总公司 Oxygen-containing coal layer gas deoxygenation denitrogenation liquefaction process
CN105605883A (en) * 2016-03-25 2016-05-25 北京中科瑞奥能源科技股份有限公司 Oxygen-bearing coalbed methane liquefaction separation system and technique
CN109294647A (en) * 2018-09-17 2019-02-01 广州智光节能有限公司 The purification system of natural gas

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CN103484184A (en) * 2013-09-05 2014-01-01 中国海洋石油总公司 Deoxidation and denitrification system for oxygen-containing coal bed gas
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CN105605883A (en) * 2016-03-25 2016-05-25 北京中科瑞奥能源科技股份有限公司 Oxygen-bearing coalbed methane liquefaction separation system and technique
CN109294647A (en) * 2018-09-17 2019-02-01 广州智光节能有限公司 The purification system of natural gas

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